The Party chief of North China's Shanxi Province said on Tuesday that 20,000 officials have voluntarily surrendered ill-gotten wealth worth over 170 million yuan ($25.9 million) to the provincial disciplinary watchdog as of April, but said some officials have refused to confess.

During an interview with the website of the Communist Party of China's Central Commission for Discipline Inspection (CCDI) on Tuesday, Wang Rulin said as of April, 5,646 officials have confessed to violating Party rules, and officials handed in "red packets", which are normally used for monetary gifts, to authorities.

Wang said five Party chiefs of cities in Shanxi have been investigated in the past year. Before that no Party chiefs had been probed in the last 14 years.

He said the anti-corruption campaign has been focused on department heads involved in coal, land resources, environmental protection and transportation, as well as from Lüliang and Gaoping, according to the transcript posted on CCDI's website.

Disciplinary watchdogs at all levels in the province saw a 17.6 percent drop in tips in the first quarter compared to the same period the previous year, Wang said.

"Certain officials attempted to cover their tracks, refuse to confess or even cooperate with disciplinary watchdogs, although a majority of Party officials have a clear picture of the situation and seized on the opportunity under the anti-graft campaign," Wang was quoted by CCDI's website as saying.

He pointed out in March that such corruption has not only severely dampened the province's economic development but also damaged relations between officials and the public, and jeopardized the Party's ruling foundation.

Shanxi is one of China's major coal producers and contributes greatly to the country's energy supply.

In 2014, seven of the province's top leaders were put under investigation.

Party committees should be held accountable for rampant corrupt cases in Shanxi, Huang Shuxian, CCDI vice secretary, was quoted by the Xinhua News Agency as saying in January 2015.